A Novel Plan for Increasing Well Supply

A Novel Plan for Increasing Well Supply

How the City of Winner, S. Dak., Met Problem of Need for More Water—Method of Building Trench—Water Level of the Gallery

THERE are undoubtedly many smaller cities and towns with similar problems in water supply to that of the municipality referred to in this paper, and the description should provide some suggestions as to the best means of meeting difficulties which parallel those of the city of Winner.

The City of Winner, S. Dale., is located in a district in which it is difficult to obtain water in large amounts sufficient for public water supplies. Such water as is obtainable is to be found underground. The sub-soil generally is of a very fine sandy nature that makes it difficult to obtain the water because of the packing and encrusting nature of the fine sand sub-soil about the strainers employed in connection with the tubular wells.

The city has in the past been depending upon water for its public needs that is obtained principally from two 24-inch Kelly wells sunk to a depth of about 28 feet and reinforced by about 15 wells of 6-inch tubular type that were sunk approximately 28 feet. All of these wells are connected to an 8-inch water main that was laid at a depth of approximately 8 feet below the surface of the ground.

This well system is located about 8 1/2 miles south of the city of Winner on ground about 80 feet above the elevation of two circular concrete reservoirs that are located about one mile south of the center of the town, and that afford a static pressure in the business section of the city of about 60 pounds per square inch. The connecting pipe between the reservoirs and the well system is an 8-inch machine banded wooden pipe.

There are no authentic records indicating the amount of water used in the city of Winner which has a population of approximately 2,500; the nearest estimate would indicate from 100,000 to 125,000 gallons per 24 hours, and this amount of water has had to be pumped in recent years from the two 24-inch Kelly wells, the fifteen small er tubular wells having Cook strainers have not afforded any water as the sand bed from which the water is obtained is very fine, the coarsest being about like granulated sugar and this sand has become encased around the screens to such an extent that the tubular wells have practically been useless for some years.

Engineers Submit Plans

Because of a shortage of water the city authorities employed a number of engineers to submit reports upon ways and means that might be employed to enlarge the amount of water for public purposes, and the writer submitted tentative plans for obtaining the desired additional water supply, which were finally adopted and approved by the council of the city of Winner. A contract was effected between the _____v and an Omaha contracting firm based upon detail plans specifications formulated by the writer, which em_____ed the following plan of procedure:

It was believed that the fineness of the sand sub-soil precluded the use of open jointed or perforated underground pipe lines and in place of employing such a type of construction, it was decided to adopt that of an open trench which was to he excavated across the draw in which the aforesaid wells were located. This draw is about 500 feet in width and experience indicates that a large portion of the drainage from 20 square miles located above and to the south of the said system of wells passes as underflow below the draw in which the wells are located and about 15 to 25 feet below the ground level.

The Plans as Adopted

The adopted plans considered excavating a trench across the draw having a width of 6 feet inside and a depth of about 15 feet below ground level, the trench to be sheathed with 4 inch thickness of sheathing plank that was made up by nailing together two 2-inch planks, the planks being so lapped so as to leave at least 6 inches. The two planks being thus muled together for their entire length with their 6-inch lap formed a couple, and contiguous couples on either side made it possible to make tight work, each couple lapping the companion by 6 inches. These planks nailed together in couples were first sunk by water jet to the required depth. The sheathing forming the upper or south line of trench was sunk to a depth of 18 feet below the bottom of the trench when excavated and those forming the lower or north side of the trench were sunk approximately 22 feet below ground level or about 7 feet below the bottom of the trench as excavated, thus forming a submerged timber cut-off against the passage of water.

Depth of the Trench

The trench was afterwards excavated as stated to a depth of about 15 feet below ground level, the sides of the trench being firmly braced by longitudinal and transverse members as the excavation proceeded, said bracing being spaced from 3 to 4 feet apart vertically.

The purpose of making this trench 6 feet in width was primarilly to make it possible to sink Kelly wells to a depth below the bottom of the trench should it develop that such a measure would be necessary to secure the desired amount of water.

The sheathing plank at the east end of the trench for a distance of 10 feet were sunk to a depth of 24 feet below ground level. The reason for sinking the plank sheathing deeper at the east end was to provide a sand pocket into which sand that might be held in suspension in the water would be deposited before entering the outlet pipe, which is connected with the sand pocket at an elevation approximately 15 feet below ground level.

The tops of all sheathing plank were sunk to a depth of two feet below ground level and furnishes a support upon which was placed a 6-inch steel reinforced concrete cover that extends for the full length and width of the collecting gallery. The gallery is 300 feet long.

Manholes for Entrance to Gallery

Five manholes have been constructed of concrete which extend above the concrete cover to ground level upon which iron frames and covers have been placed to afford means of entering the gallery should occasion require for inspection and possible removal of sand.

Over the concrete slab there has been placed earth filling to an elevation slightly above ground level to allow for settling, this earth filling has a 6 inch topping of black soil and will be seeded so that the gallery will be covered by grass sod and present a smooth surface with the surrounding field.

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Water Level of Gallery

The water level in the gallery when no water is being drawn stands approximately 4 feet below ground level, and it is believed that the sheathing plank will last indefinitely under these damp conditions. If, however, in years to come it is necessary to replace the tops of the plank sheathing, this can be done at small expense.

The water level with the gallery in service is drawn down about 4 to 5 feet, and it is believed that this collecting gallery will afford an ample supply for the needs of the city for some years in the future. At present the city is not using the amount that the gallery will afford, which at present is approximately 300 gallons per minute.

In order to deliver the water from the gallery at a depth of 15 feet below ground level it was necessary to lay 2,500 feet of 10 inch cast iron pipe connecting with the existing 8 inch machine banded wood pipe, whereby, it is possible now for the city to dispense entirely with pumping its water supply, the water being delivered by gravity into two concrete circular reservoirs, each having a capacity of approximately 80,000 gallons.

Such in brief is a description of the methods adopted to obtain the required additional water supply. The cost for 300 feet of collecting gallery complete was $11,500.00.

(Excerpts from paper read before the annual convention of the Iowa Section, American Water Works Association.)

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